Monday was Jackson's best outing of the spring.
"I'm just trying to progress as the season goes on," Jackson said. "I'm just trying to get closer to game mode as we get closer to the end of March, and I'm just trying to keep the ball rolling in a positive direction right on into the season."
His goal is to make his infielders work.
"It's hard to hit a home run on the ground so you try to keep the ball down," Jackson said.
One thing he does have to work on is packing. Jackson wore jersey No. 82, not his assigned No. 36. He forgot that one.
"I was coming out as a new person to try out," Jackson said, joking about the mistake. "I had my bag packed an hour before, too. The number didn't do me too bad."
Usually No. 82 is reserved for Minor Leaguers or non-roster invitees. Will Jackson wear it again?
"I don't know about that," Jackson said.
San Diego pitcher Clayton Richard allowed one run over the first three innings before allowing the three-run shot in the fifth inning to Sappelt. It was Sappelt's third home run of the spring.
Richard allowed five runs on seven hits with no walks and four strikeouts in 6 2/3 innings. It was his longest start of the spring and the longest outing by any Padres pitcher.
The Cubs (11-14) took a 1-0 lead in the fourth inning when Darnell McDonald singled and stole second base. He advanced to third base on a ground ball to the right side and then scored on a groundout by Javier Baez.
First baseman Brent Lillibridge had two hits for the Cubs, including a triple to start the seventh inning. He scored on an Alberto Gonzalez sacrifice fly to make it 5-1.
The Padres (12-13) got two hits from leadoff hitter Everth Cabrera and an RBI single by Richard in the fifth inning. It was Richard's first hit of the spring.
Cubs Up Next: Lefty Chris Rusin will make his third start and appear in his fifth spring game on Tuesday when the Cubs play host to the Rangers at HoHoKam Stadium. He has given up one run on eight hits and one walk over 13 innings, striking out eight. Want to know the Cubs' Opening Day lineup? You'll get a preview Tuesday: David DeJesus will lead off and play center, followed by shortstop Starlin Castro, first baseman Anthony Rizzo, left fielder Alfonso Soriano, right fielder Nate Schierholtz, catcher Welington Castillo, third baseman Luis Valbuena and second baseman Darwin Barney. The game will be broadcast on Cubs.com.